Lithofacies paleogeography in the depositional period of the Datangpo Formation of Nanhua System in the Middle and Upper Yangtze Region, SW China and its indication of hydrocarbon accumulation

[Objective]Marine black manganese-bearing carbonaceous shale of Datangpo Formation was generally developed in the mid-Neoproterozoic Nanhua period in the Middle-Upper Yangtze Region, South China, which has been widely concerned as a manganese deposit for a long time, but with little attention to its petroleum geological characteristics. This paper expounds the lithofacies paleogeography of the Datangpo Formation and its indication of oil and gas accumulation, so as to guide the oil and gas investigation in the Suthern China.[Methods] Through field investigation and data collection on the Datangpo Formation, the oil and gas geological conditions, the source rock characteristics and hydrocarbon accumulation assemblage, especially lithofacies and paleogeography, were systematically analyzed by methods of single well analysis, continuous well comparison, lithofacies paleogeographic map compilation, etc., combined with source rock characteristic analysis, reservoir analysis and other experimental testing methods.[Results] The Datangpo Formation was formed during the interglacial period, and the depositional process was controlled by the extensional rifting process. Its sedimentary facies can be divided into two types, seven subtypes and several microfacies. The entire depositional period constitutes a complete transgressive-Highstand-Regressive sedimentary cycle; the most potential facies belts for oil and gas resources in the Datangpo Formation are limited shelf subfacies and lagoon subfacies, mainly distributed in the first member, with good organic geochemical index characteristics, and are high-quality source rocks.[Conclusions] The first member of the Datangpo Formation has good hydrocarbon generation and shale gas development potential. Songtao, Huayuan, Xiushan, Xiangtan, Hefeng and other areas at the junction of Hunan, Chongqing and Guizhou Province have favorable conditions for shale gas development and are potential shale gas development areas. With the Datangpo Formation as the source rock, a variety of potential reservoir-forming assemblages can be formed. The Xiushan, Songtao and Huayuan areas at the junction of Chongqing, Guizhou and Hunan Province have good source-reservoir configuration conditions and are potential conventional oil and gas development areas.